The Build Hotbar (bottom center) now has a button you can press to open up a panel that shows all 10 of your available build hotbar slots!
This is where the button is:
...And it opens this panel, letting you select an active hotbar row.
Note: you can also access this from the editable hotbar that appears when you open the Build menu. Just hit the button that says "Build Hotbar #1"
The game still lets you use F1-F4 to select the first four hotbar rows, and Alt+Num to select any of the 10. But it's not obvious this feature exists, so it's worth pointing it out here!
Fixed bug: items in pipes that were crossing the underground / aboveground line were not drawn at the correct height
Prevented non-buildable items from being dragged and dropped into the build hotbar. Dragging a buildable item will assign the buildable version of the item you dragged (e.g. a Fluid Pipe 'Item' gets turned into a Fluid Pipe 'Structure'). If any legacy maps had items on the build hotbar inadvertently, they are converted to the buildable version if possible. Otherwise they are automatically removed from the build hotbar (as it can cause lots of errors if you try to build something like a Banana)
Added text tooltips to items in the Inventory hotbar to tell you what the item is